1. Field of the Invention
The present invention relates to a thermal activation device, a printing device, and a printer for conveying, by a platen roller, a sheet material having a print layer on one surface of the sheet material and a heat-sensitive adhesive layer on other surface thereof.
2. Related Background Art
In distribution of goods and stores, for instance, a label indicating various types of information such as prices or bar-code for management use output by a POS (point of sales) terminal is adhered on goods. For this type of label, a label formed of a sheet material including a print layer on one surface of a sheet-like base material and a heat-sensitive adhesive layer on the other surface thereof is proposed.
As a general label issuing device for issuing a label having such a heat-sensitive adhesive layer, an arrangement including a sheet supplying device for supplying a sheet material, a printing device for printing various types of information on a heat-sensitive print layer of the sheet material supplied from the sheet supplying device, a cutting device for cutting the sheet material printed by the printing device, and a thermal activation device for thermally activating the heat-sensitive adhesive layer of the sheet material is disclosed.
As illustrated in FIG. 8, the thermal activation device includes a thermal activation head 111 for thermally activating the heat-sensitive adhesive layer of the sheet material, a platen roller 112 with which the thermal activation head 111 is brought into press-contact, and for holding and conveying the sheet material, and a head support member 113 for supporting the thermal activation head 111.
The platen roller 112 is supported by a platen shaft 118 in a rotatable manner supported by a support frame (not shown), and is driven to rotate by a rotary drive mechanism, not shown. In addition, the head support member 113 is provided with the thermal activation head 111 on one end thereof and a pair of support pieces 119 supported in a rotatable manner by a shaft 114 supported by a support frame. Each of support pieces 119 is provided with a shaft hole 115 into which the shaft 114 is inserted. In addition, a plurality of platen springs 116 for causing the thermal activation head 111 to be in press-contact with a circumference surface of the platen roller 112 is provided on the opposite side of the platen roller 112 across the head support member 113.
With the thermal activation device, a heat-sensitive adhesive layer is thermally activated by the thermal activation head 111 and the sheet material pinched between the thermal activation head 111 and the platen roller 112 is conveyed by the rotation of the platen roller 112 with which the thermal activation head 111 is brought into press-contact.
In addition, although it is not illustrated in the figures, similar to the thermal activation device, the printing device also includes a print head for printing on a heat-sensitive printing layer of the sheet material, a platen roller with which the print head is brought into press-contact for holding and conveying the sheet material, and a head support member for supporting the print head. The head support member is supported, via a support shaft, by a support frame in a rotatable manner and the print head is brought into press-contact with the platen roller by an urging force of a platen spring.
As described above, in a conventional thermal activation device or a printing device, a head support member for supporting a thermal activation head or a print head (hereinafter, simply referred to as a head) is supported by a support frame via a support shaft in a rotatable manner. For this reason, when dimensional accuracy of the head support member or the support frame is not favorably maintained due to manufacturing variation, a platen shaft for supporting a platen roller in a rotatable manner and the support shaft for supporting the head support member in a rotatable manner may not be in parallel to each other in some cases.
In such a case, as illustrated in FIG. 9, the thermal activation head 111 is not brought into contact with the platen roller 112 all over it in an axial direction of the support shaft 114, but is in an uneven contact state in which only one end of the thermal activation head 111 in the axial direction of the shaft 114 is brought into contact with the sheet material.
For this reason, as to the sheet material to be conveyed by the platen roller, only one end of the sheet material in the width direction perpendicular to the conveyance direction may be favorably pressed by the head, however, the other end of the sheet material may not be favorably pressed by the head, resulting in an insufficient pressing force of the head exerted onto the sheet material. That is, a gap is formed between the platen roller and the thermal activation head, and a press-contact state of the sheet material relative to the head becomes insufficient, causing a problem of occurrence of thin spots in the sheet material.
As a measure for solving such problems, a method of correcting uneven contact of the head with respect to the sheet material in a direction of the support shaft, by increasing the press-contact force of the head with the platen roller by increasing the urging force of the platen spring is considered. In some cases, however, the press-contact force may be increased more than necessary due to manufacturing variation, or the press-contact force may not be sufficiently obtained, and thus, it is difficult to sufficiently eliminate uneven contact of the head with respect to the sheet material only by increasing the urging force of the platen spring.
In addition, in the above-described sheet material including the heat-sensitive adhesive layer, a friction coefficient of the heat-sensitive adhesive layer is very large compared to the friction coefficient of the heat-sensitive print layer. For this reason, particularly in the thermal activation device, when conveying the heat-sensitive adhesive sheet, the friction force between the heat-sensitive adhesive layer and the thermal activation head becomes larger than the friction force between the platen roller and the print layer, and so the platen roller is idly rotated relative to the sheet material and therefore it becomes difficult to smoothly convey the sheet material at a predetermined conveyance speed.
For this reason, particularly in the thermal activation device, when the urging force of the platen spring is increased as described above so as to eliminate uneven contact of the thermal activation head with respect to the sheet material, it leads to a problem in which the heat-sensitive adhesive layer of the sheet material is apt to adhere to the thermal activation head. Consequently, in the thermal activation device, the problem of eliminating the uneven contact of the thermal activation head with respect to the sheet material in the direction of the support shaft may not be solved just by increasing the urging force of the platen spring.